Differential regulation of proinflammatory mediators following LPS- and ATP-induced activation of monocytes from patients with antiphospholipid syndrome

NLRP3-Induced NETosis: A Potential Therapeutic Target for Ischemic Thrombotic Diseases?

Ischemic thrombotic disease, characterized by the formation of obstructive blood clots within arteries or veins, is a condition associated with life-threatening events, such as stroke, myocardial infarction, deep vein thrombosis, and pulmonary embolism. The conventional therapeutic strategy relies on treatments with anticoagulants that unfortunately pose an inherent risk of bleeding complications. These anticoagulants primarily target clotting factors, often overlooking upstream events, including the release of neutrophil extracellular traps (NETs). Neutrophils are integral components of the innate immune system, traditionally known for their role in combating pathogens through NET formation. Emerging evidence has now revealed that NETs contribute to a prothrombotic milieu by promoting platelet activation, increasing thrombin generation, and providing a scaffold for clot formation. Additionally, NET components enhance clot stability and resistance to fibrinolysis. Clinical and preclinical studies have underscored the mechanistic involvement of NETs in the pathogenesis of thrombotic complications, since the clots obtained from patients and experimental models consistently exhibit the presence of NETs. Given these insights, the inhibition of NETs or NET formation is emerging as a promising therapeutic approach for ischemic thrombotic diseases. Recent investigations also implicate a role for the nucleotide-binding oligomerization domain (NOD)-like receptor family pyrin domain-containing 3 (NLRP3) inflammasome as a mediator of NETosis and thrombosis, suggesting that NLRP3 inhibition may also hold potential for mitigating thrombotic events. Therefore, future preclinical and clinical studies aimed at identifying and validating NLRP3 inhibition as a novel therapeutic intervention for thrombotic disorders are imperative.

The role of monocytes in thrombotic diseases: a review

Cardiovascular and cerebrovascular diseases are the number one killer threatening people's life and health, among which cardiovascular thrombotic events are the most common. As the cause of particularly serious cardiovascular events, thrombosis can trigger fatal crises such as acute coronary syndrome (myocardial infarction and unstable angina), cerebral infarction and so on. Circulating monocytes are an important part of innate immunity. Their main physiological functions are phagocytosis, removal of injured and senescent cells and their debris, and development into macrophages and dendritic cells. At the same time, they also participate in the pathophysiological processes of pro-coagulation and anticoagulation. According to recent studies, monocytes have been found to play a significant role in thrombosis and thrombotic diseases of the immune system. In this manuscript, we review the relationship between monocyte subsets and cardiovascular thrombotic events and analyze the role of monocytes in arterial thrombosis and their involvement in intravenous thrombolysis. Finally, we summarize the mechanism and therapeutic regimen of monocyte and thrombosis in hypertension, antiphospholipid syndrome, atherosclerosis, rheumatic heart disease, lower extremity deep venous thrombosis, and diabetic nephropathy.

Antiphospholipid antibodies induce proinflammatory and procoagulant pathways in endothelial cells

Antiphospholipid syndrome (APS) is an autoimmune thrombophilia characterized by recurrent thrombotic events and/or pregnancy morbidity in the presence of antiphospholipid antibodies detected either as anti-cardiolipin, anti-β2 Glycoprotein I (anti-β2GPI) or Lupus anticoagulant (LA). Endothelial deregulation characterizes the syndrome. To address gene expression changes accompanying the development of autoimmune phenotype in endothelial cells in the context of APS, we performed transcriptomics analysis in Human Umbilical Vein Endothelial Cells (HUVECs) stimulated with IgG from APS patients and β2GPI, followed by intersection of RNA-seq data with published microarray and ChIP-seq results (Chromatin Immunoprecipitation). Our strategy revealed that during HUVEC activation diverse signaling pathways such as TNF-α, TGF-β, MAPK38, and Hippo are triggered as indicated by Gene Ontology (GO) classification and pathway analysis. Finally, cell biology approaches performed side-by-side in naïve and stimulated cultured HUVECs, as well as, in placenta specimens derived from Healthy donors (HDs) and APS-patients verified the evolution of an APS-characteristic gene expression program in endothelial cells during the initial stages of the disease's development.

Targeting thromboinflammation in antiphospholipid syndrome

Antiphospholipid syndrome (APS) is a systemic autoimmune disease, where persistent presence of antiphospholipid antibodies (aPL) leads to thrombotic and obstetric complications. APS is a paradigmatic thromboinflammatory disease. Thromboinflammation is a pathophysiological mechanism coupling inflammation and thrombosis, which contributes to the pathophysiology of cardiovascular disease. APS can serve as a model to unravel mechanisms of thromboinflammation and the relationship between innate immune cells and thrombosis. Monocytes are activated by aPL into a proinflammatory and procoagulant phenotype, producing proinflammatory cytokines such as tumor necrosis factor α, interleukin 6, as well as tissue factor. Important cellular signaling pathways involved are the NF-κB-pathway, mammalian target of rapamycin (mTOR) signaling, and the NOD-, LRR-, and pyrin domain-containing protein 3 inflammasome. All of these may serve as future therapeutic targets. Neutrophils produce neutrophil extracellular traps in response to aPL, and this leads to thrombosis. Thrombosis in APS also stems from increased interaction of neutrophils with endothelial cells through P-selectin glycoprotein ligand-1. NETosis can be targeted not only with several experimental therapeutics, such as DNase, but also through the redirection of current therapies such as defibrotide and the antiplatelet agent dipyridamole. Activation of platelets by aPL leads to a procoagulant phenotype. Platelet-leukocyte interactions are increased, possibly mediated by increased levels of soluble P-selectin and soluble CD40-ligand. Platelet-directed future treatment options involve the inhibition of several platelet receptors activated by aPL, as well as mTOR inhibition. This review discusses mechanisms underlying thromboinflammation in APS that present targetable therapeutic options, some of which may be generalizable to other thromboinflammatory diseases.

miR-19b-3p and miR-20a-5p are associated with the levels of antiphospholipid antibodies in patients with antiphospholipid syndrome

Monocytes play a key role in pathophysiology of antiphospholipid syndrome (APS), nevertheless it is unclear if microRNA expression is associated with particular APS features. Identify whether miR-19b-3p and miR-20a-5p expression in monocytes are associated with hallmarks of the APS. Fifty-seven APS patients and 18 healthy controls were studied. Expression of miR-19b-3p and miR-20a-5p was measured in monocytes by RT-qPCR. Both miR-19b-3p (AUC = 0.835, 95% CI 0.733-0.938; P < 0.001) and miR-20a-5p (AUC = 0.857, 0.757-0.957; P < 0.001) discriminated APS patients from healthy individuals. A cut-off point of 1.98 for miR-19-3p and 2.18 for miR-20a-5p showed that APS patients with low microRNA expression had higher levels of IgM and IgG anticardiolipin antibodies than patients with high microRNA expression. In addition, APS patients with low microRNA expression had higher IgG anti-β₂ glycoprotein I antibody levels than their counterparts with high microRNA expression. Finally, miR-19b-3p and miR-20a-5p expression levels were significantly higher in APS patients using oral anticoagulants. Monocyte expression of miR-19b-3p and miR-20a-5p is low in APS, and patients with the lowest microRNA expression presented the highest levels of antiphospholipid antibodies.

Immunosuppressive Treatment in Antiphospholipid Syndrome: Is It Worth It?

The antiphospholipid syndrome (APS) is characterized by the development of venous and/or arterial thrombosis and pregnancy morbidity in patients with persistent antiphospholipid antibodies (aPL). Catastrophic antiphospholipid syndrome (CAPS) is a life-threatening form of APS occurring in about 1% of cases. Lifelong anticoagulation with vitamin K antagonists remains the cornerstone of the therapy for thrombotic APS, but frequently the use of anticoagulation may be problematic due to the increased risk of bleeding, drug interactions, or comorbidities. Immunosuppressant drugs are widely used to treat several autoimmune conditions, in which their safety and effectiveness have been largely demonstrated. Similar evidence in the treatment of primary APS is limited to case reports or case series, and studies on a large scale lack. Immunomodulatory drugs may be an emerging tool in managing such particular situations, like refractory obstetrical complications, CAPS, or so-called APS non-criteria manifestations. In addition, immunomodulatory drugs may be useful in patients experiencing recurrent thromboembolic events despite optimized anticoagulant therapy. We did a comprehensive review of literature analyzing the possible role of immunomodulation in primary APS to provide a broad overview of potentially safe and effective target treatments for managing this devastating disease.

Expression of tissue factor mRNA in thrombosis associated with antiphospholipid syndrome

Tissue factor (TF) is a procoagulant protein associated with increased risk of thrombotic events in antiphospholipid syndrome (t-APS). The mechanisms by which TF levels are increased in APS have not yet been established. The aim of this study was to investigate whether TF mRNA expression is associated with TF levels and thrombosis in APS. We compared levels of circulating TF and high sensitivity C-reactive protein (hs-CRP) between t-APS and controls (individuals without thrombosis). The association between TF mRNA expression, quantified by real time quantitative polymerase chain reaction, and t-APS was accessed using regression analysis. We included 41 controls and 42 t-APS patients, mean age was 41 years old (SD 14) in both groups. Hs-CRP and TF levels were higher in t-APS patients (mean hs-CRP levels 0.81 mg/dL [SD 1.88] and median TF levels 249.0 pg/mL [IQR 138.77-447.61]) as compared to controls (mean hs-CRP levels 0.24 mg/dL [SD 0.26] and median TF levels 113.0 pg/mL [IQR 81.17-161.53]; P = 0.02 and P < 0.0001, respectively). There was no correlation between TF mRNA expression and TF levels in t-APS (r - 0.209, P = 0.19). TF mRNA expression was not associated with t-APS (adjusted OR 1.16; 95%CI 0.72-1.87). Despite circulating TF levels being higher in patients with t-APS than in controls, TF mRNA expression was similar between groups. The results demonstrate that TF mRNA expression is not associated with levels of circulating TF and hypercoagulability in t-APS.

Anti-domain 1 β2 glycoprotein antibodies increase expression of tissue factor on monocytes and activate NK Cells and CD8+ cells in vitro

Background

β2-Glycoprotein I (β2GPI) represents the major antigenic target for antiphospholipid antibodies (aPL), with domain 1 (D1) being identified as a risk factor for thrombosis and pregnancy complications in APS. We aimed to analyse the ability of aPL, and particularly anti-D1 β2GPI, to stimulate prothrombotic and proinflammatory activity of immune cells in vitro.

Methods

Peripheral blood mononuclear cells (PBMCs) from 11 healthy individuals were incubated with: (1) “anti-D1(+)”—pooled plasma derived from patients suspected of having APS contained anticardiolipin antibodies (aCL), lupus anticoagulant (LA), anti-β2GPI and anti-D1 β2GPI; (2) “anti-D1(−)”—pooled plasma from patients suspected of having APS contained aCL, LA, anti-β2GPI, and negative for anti-D1 β2GPI; (3) “seronegative”—negative for aPL.

Results

The presence of anti-D1(+) and anti-D1(−) plasma resulted in increased HLA-DR and CD11b on monocytes. While only anti-D1(+) plasma markedly increased the percentage and median fluorescence intensity (MFI) of CD142 (tissue factor, TF) on monocytes in comparison with those cultured with anti-D1(−) and seronegative plasma. Anti-D1(+) plasma resulted in increased percentage and MFI of activation marker CD69 on NK and T cytotoxic cells. Expression of IgG receptor FcγRIII(CD16) on monocytes and NK cells was down-regulated by the anti-D1(+) plasma.

Conclusions

Taking together, our study shows the ability of patient-derived aPL to induce immune cell activation and TF expression on monocytes. For the first time, we demonstrated the influence of anti-D1 β2GPI on the activation status of monocytes, NK and cytotoxic T cells. Our findings further support a crucial role of D1 epitope in the promotion of thrombosis and obstetrical complications in APS.

Environmental Triggers of Autoreactive Responses: Induction of Antiphospholipid Antibody Formation

Antiphospholipid antibodies (aPLs) comprise a diverse family of autoantibodies targeted against proteins with the affinity toward negatively charged phospholipids or protein-phospholipid complexes. Their clinical significance, including prothrombotic potential of anti-cardiolipin antibodies (aCLs), anti-β2-glycoprotein I antibodies (aβ2-GPIs), and lupus anti-coagulant (LA), is well-established. However, the ontogeny of these pathogenic aPLs remains less clear. While transient appearance of aPLs could be induced by various environmental factors, in genetically predisposed individuals these factors may eventually lead to the development of the antiphospholipid syndrome (APS). Since the first description of APS, it has been found that a wide variety of microbial and viral agents influence aPLs production and contribute to clinical manifestations of APS. Many theories attempted to explain the pathogenic potential of different environmental factors as well as a phenomenon termed molecular mimicry between β2-GPI molecule and infection-relevant structures. In this review, we summarize and critically assess the pathogenic and non-pathogenic formation of aPLs and its contribution to the development of APS.

Elevated plasma level of soluble triggering receptor expressed on myeloid cells-1 is associated with inflammation activity and is a potential biomarker of thrombosis in primary antiphospholipid syndrome

Background

Soluble triggering receptor expressed on myeloid cells-1 (sTREM-1) is an innate-immune receptor found in blood. Its presence reflects innate immune cell activation. We sought to investigate plasma sTREM-1 levels in patients with primary antiphospholipid syndrome (PAPS).

Methods

A cross-sectional, case-control design was used. Plasma sTREM-1 levels were analyzed by enzyme-linked immunosorbent assay (ELISA) in consecutive patients diagnosed with PAPS or asymptomatic antiphospholipid antibody (APLA) carriers and controls.

Results

The study cohort included 33 patients with PAPS, 10 asymptomatic APLA carriers, and 73 controls. Mean plasma sTREM-1 levels were significantly higher in patients with PAPS (299.2 ± 146.7 pg/ml) and thrombotic PAPS-ever (current and past thrombotic event) (327.2 ± 151.3 pg/ml) compared with controls (230.2 ± 85.5 pg/ml; p = 0.006 and p = 0.003, respectively), patients with thrombotic PAPS compared with patients with past obstetric APS (195.12 ± 58.52 pg/ml, p = 0.01) and APLA carriers (215.8 ± 51.6 pg/ml, p = 0.02), patients with current thrombotic PAPS (429.5 ± 227.5 pg/ml) compared with patients with past thrombotic PAPS (289.5 ± 94.65 pg/ml, p = 0.01), and patients with PAPS who had ever had a stroke or venous thromboembolic event compared with patients who had not (p = 0.007 and p = 0.02, respectively). On receiver operator characteristic curve analysis, plasma sTREM-1 levels differentiated patients with current thrombotic PAPS from asymptomatic APLA carriers and controls, with an area under the curve of 0.7292 (p = 0.0014) and 0.88 (p < 0.0001), respectively. Multivariate regression analysis to identify sTREM-1 predictors (thrombotic PAPS-ever, age, and sex) yielded an independent association of sTREM-1 levels with thrombotic PAPS (p < 0.0001).

Conclusions

Plasma sTREM-1 levels are significantly elevated in patients with thrombotic PAPS. Levels of sTREM-1 might serve as a biomarker for thrombosis in patients with PAPS.

Circulating levels of tissue factor and the risk of thrombosis associated with antiphospholipid syndrome

The mechanisms behind the severe hypercoagulable state in antiphospholipid syndrome (APS) have not yet been fully elucidated. Knowledge on the etiology of thrombosis in APS is needed to improve treatment. We performed a case control study to evaluate the association of the levels of circulating tissue factor (TF) with thrombotic APS and unprovoked venous thromboembolism (VTE), as compared with controls without a history of thrombosis. Study participants were selected in the same geographic area. Linear regression was used to evaluate possible determinants of TF levels among controls and logistic regression was used to evaluate the association between TF, unprovoked VTE and t-APS. TF levels were grouped into three categories based on: below 50th percentile [reference], between 50-75th percentiles [second category] and 75th percentile [third category]. Two hundred and eighty participants were included in the study; 51 patients with unprovoked VTE, 111 patients with t-APS and 118 control individuals. The levels of TF were not associated with an increased risk of unprovoked VTE, as compared with controls. The adjusted odds ratio for t-APS was 2.62 (95%CI 1.03 to 6.62) with TF levels between 50-75th percentiles and 8.62 (95%CI 3.76 to 19.80) with TF levels above the 75th percentile, as compared with the reference category (below the 50th percentile). In the subgroup analysis, higher levels of TF were associated with both arterial and venous thrombosis in APS and with both primary and secondary APS. Circulating TF is associated with thrombotic complications related to APS, but not with the risk of unprovoked VTE.

Electronegative LDL induces priming and inflammasome activation leading to IL-1β release in human monocytes and macrophages

BACKGROUND

Electronegative LDL (LDL(−)), a modified LDL fraction found in blood, induces the release of inflammatory mediators in endothelial cells and leukocytes. However, the inflammatory pathways activated by LDL(−) have not been fully defined. We aim to study whether LDL(−) induced release of the first-wave proinflammatory IL-1β in monocytes and monocyte-derived macrophages (MDM) and the mechanisms involved.

METHODS

LDL(−) was isolated from total LDL by anion exchange chromatography. Monocytes and MDM were isolated from healthy donors and stimulated with LDL(+) and LDL(−) (100 mg apoB/L).

RESULTS

In monocytes, LDL(−) promoted IL-1β release in a time-dependent manner, obtaining at 20 h-incubation the double of IL-1β release induced by LDL(−) than by native LDL. LDL(−)-induced IL-1β release involved activation of the CD14-TLR4 receptor complex. LDL(−) induced priming, the first step of IL-1β release, since it increased the transcription of pro-IL-1β (8-fold) and NLRP3 (3-fold) compared to native LDL. Several findings show that LDL(−) induced inflammasome activation, the second step necessary for IL-1β release. Preincubation of monocytes with K+ channel inhibitors decreased LDL(−)-induced IL-1β release. LDL(−) induced formation of the NLRP3-ASC complex. LDL(−) triggered 2-fold caspase-1 activation compared to native LDL and IL-1β release was strongly diminished in the presence of the caspase-1 inhibitor Z-YVAD. In MDM, LDL(−) promoted IL-1β release, which was also associated with caspase-1 activation.

CONCLUSIONS

LDL(−) promotes release of biologically active IL-1β in monocytes and MDM by induction of the two steps involved: priming and NLRP3 inflammasome activation.

SIGNIFICANCE

By IL-1β release, LDL(−) could regulate inflammation in atherosclerosis.

Delineating the deranged immune system in the antiphospholipid syndrome

The antiphospholipid syndrome (APS) is a systemic autoimmune disease that is characterized serologically by the presence of antiphospholipid antibodies (aPL) and clinically by vascular thrombosis and obstetric complications. The protein β2 glycoprotein I (β2GPI) is identified as the most important autoantigen in this syndrome. Activation of endothelial cells, thrombocytes and placental tissue by anti-β2GPI antibodies relates to the clinical manifestations of APS. This review describes genetic and environmental factors in relation to APS and summarizes the current knowledge on abnormalities in components of both the innate and adaptive immune system in APS. The role of dendritic cells, T-cells, B-cells, monocytes, neutrophils and NK-cells as well as the complement system in APS are discussed. Several gaps in our knowledge on the pathophysiology of APS are identified and a plea is made for future extensive immune cell profiling by a systems medicine approach in order to better unravel the pathogenesis of APS, to gain more insight in the role of the immune system in APS as well as having the potential to reveal biomarkers or novel therapeutic targets.